【０００１】
【発明の属する技術分野】
本発明は、強誘電体等の酸化物材料を熱処理するときに、上下の電極ともに接触させないで離して行うか、どちらか一方の電極だけを離して電界を印加することにより、強誘電体等の酸化物材料の結晶配向性を高めるとともに、リーク電流特性、強誘電体特性等の電気的特性を向上させる製造方法に関するものである。
【０００２】
【従来の技術】
強誘電体等の酸化物膜を成膜する方法として、ゾルゲル法、スパッタリング法、ＭＯＣＶＤ法、ドクターブレード法等がある。このうちゾルゲル法は、最も安価かつ簡便に強誘電体等の酸化物膜を成膜できる。ゾルゲル法では、通常、金属アルコキシドを含む前駆体溶液を、スピンコートやディップコートにより成膜し、その後、熱処理炉で熱処理を施すことにより、結晶化させて製造する。熱処理の方法として、減圧加熱法、雰囲気加熱法、急速加熱法等があるが、熱処理方法により、強誘電体等の酸化物膜の結晶配向性を制御することはできない。また、スパッタリング法、ＭＯＣＶＤ法等で成膜した強誘電体等の酸化物膜を、再熱処理する場合もあるが、強誘電体等の酸化物膜の結晶配向性を制御することはできない。
【０００３】
特開平５−８５７０６の強誘電体薄膜の製造方法や特開平５−２２６３２２の配向性強誘電体薄膜の製造方法では、強誘電体薄膜に電界を印加した状態で熱処理をしているが、明細書の中で、電界を印加する電極は、薄膜にかぶせたり、スパッタ法によりＰｔ電極をつけたりして、接触させた状態で電界を印加している。
【０００４】
強誘電体等の酸化物バルク体では、通常、粉末原料を混合・成形した後、熱処理を施し、結晶化させる。熱処理方法として、ＨＩＰや急速加熱等があるが、結晶配向性を制御することはできない。
【０００５】
【発明が解決しようとする課題】
上記の従来の熱処理方法では、結晶配向性が高く、電気的特性の優れた強誘電体等の酸化物膜・バルク体が得られなかった。また、特開平５−８５７０６の強誘電体薄膜の製造方法や特開平５−２２６３２２の配向性強誘電体薄膜の製造方法で開示されている方法では、電極を接触させた状態で電界を印加しているため、ある程度の結晶配向性のある強誘電体薄膜は得られるが、薄膜中に電流が流れやすく、リーク電流により膜質が悪化してしまう。また、強誘電体は酸化物であるため、電極を接触させると、酸素を強誘電体に十分供給することができなくなり、強誘電体特性が得られるペロブスカイト相ができにくくなってしまう。これらのことから、リーク電流特性、強誘電体特性等の電気的特性の優れたものを得ることは困難である。
【０００６】
【課題を解決するための手段】
ゾルゲル法、スパッタリング法、ＭＯＣＶＤ法、ドクターブレード法等で、下部電極上に成膜した強誘電体等の酸化物膜を熱処理するときに、電界を印加する。このときの電界を印加する方法として、上部電極は強誘電体等の酸化物膜に接触させないで、離した状態で行い、膜には電流が流れないように、電場だけを印加できる構造である。
【０００７】
粉末原料を混合・成形した強誘電体等の酸化物バルク体を熱処理するときに、電界を印加する。このときの電界を印加する方法として、強誘電体等の酸化物バルク体に、上下の電極ともに接触させないで離して行うか、どちらか一方の電極だけを離した状態で行い、バルク体には電流が流れないように、電場だけを印加できる構造である。
【０００８】
【０００６】に記載の強誘電体等の酸化物薄膜に電界を印加する方法として、上部電極を強誘電体等の酸化物膜に対してさまざまな方向に配置して、さまざまな方向で電界を印加できる構造もとることができる。
【０００９】
【０００６】、
【０００７】、
【０００８】に記載した電界を印加する方法で、電界を印加する時間は、強誘電体等の酸化物材料が結晶化するときだけでも良いし、熱処理工程中であれば、全工程に渡っても、昇温時、結晶化温度保持時、降温時いかなる時でも良い。
【００１０】
【発明の実施の形態】
図１に強誘電体等の酸化物膜の電界印加構造概念図を示す。
強誘電体等の酸化物膜を成膜する方法として、ゾルゲル法、スパッタリング法、ＭＯＣＶＤ法、ドクターブレード法等がある。このうちゾルゲル法は、最も安価かつ簡便に強誘電体等の酸化物膜を成膜できる。ゾルゲル法で下部電極上に成膜した膜を、熱処理するときに電界を印加する。このときの電界を印加する方法として、上部電極は、強誘電体等の酸化物膜に接触させないで、離した状態で行う。そのようにすることにより、膜の結晶配向性を高めることができるだけでなく、電界だけを膜に印加することができるため、膜に電流は流れず、膜質も向上する。また、離した状態で行うことから、酸素を十分に膜に供給することができ、ペロブスカイト相ができやすくなる。これらのことから、結晶配向性が高く、分極方向の揃った膜が得られると同時に、リーク電流特性や強誘電体特性等の電気的特性の優れた膜が得られる。また、スパッタリング法、ＭＯＣＶＤ法等で成膜した強誘電体等の酸化物膜を再熱処理する場合にも、上記の方法で、結晶配向性が高く、分極方向の揃った膜が得られると同時に、リーク電流特性や強誘電体特性等の電気的特性の優れた膜が得られる。
【００１１】
図２に強誘電体等の酸化物バルク体の電界印加構造概念図を示す。
粉末原料を混合・成形した強誘電体等の酸化物バルク体を熱処理するときに電界を印加する。このときの電界を印加する方法として、強誘電体等の酸化物バルク体に、図２（イ）のようにどちらか一方の電極だけを離した状態で行うか、図２（ロ）のように上下の電極ともに接触させないで離して行うことにより、バルク体の結晶配向を揃えることができるだけでなく、電界だけをバルク体に印加することができるため、バルク体に電流は流れず、バルク体の特性も向上する。また、離した状態で行うことから、酸素を十分にバルク体に供給することができ、ペロブスカイト相ができやすくなる。これらのことから、結晶配向性が高く、分極方向の揃った電気的特性の優れたバルク体が得られる。
【００１２】
図３に、上部電極を強誘電体等の酸化物膜に対してさまざまな方向に配置して、さまざまな方向で電界を印加することのできる構造概念図を示す。
ゾルゲル法等で下部電極上に成膜した強誘電体膜に対して、上部電極を接触させないで離した状態で、さまざまな位置に配置させる。この状態で、焼成中に電界を印加させることにより、所望する結晶配向の揃った膜が得られると同時に、リーク特性や強誘電体特性等の電気的特性の優れた膜が得られる。
【００１３】
【実施例】
以下、本発明の実施例を、添付図面を参照して説明する。
（実施例１）
図４に強誘電体等の酸化物薄膜の電界印加構造図を示す。白金（Ｐｔ）をスパッタ法で形成した基板に、スピンコート法によりＰｂ１．２Ｌａ０．１ＴｉＯ３ （ＰＬＴ）薄膜を成膜し、乾燥、仮焼を行った。スピンコート、乾燥、仮焼を繰り返し行い、約２５０ｎｍの薄膜を得た。得られた薄膜を、図４に示すように、上部電極とＰｂ１．２Ｌａ０．１ＴｉＯ３薄膜を接触させないで、０．５ｍｍ離した状態にして、大気中、５００℃で熱処理工程中に、５Ｖの電界を印加させた。
【００１４】
このようにして、熱処理工程中に電極を接触させないで離した状態にして電界を印加した効果について、図５にＸ線回折図を示す。図中の（イ）は電界を印加していない場合、（ロ）は本実施例に基づく電界印加した場合であるが、明らかにＰＬＴの（１００）に関するピークは、（ロ）の方が強くなり、結晶配向性が高くなっていることがわかる。
【００１５】
図６に、熱処理工程中に電極を接触させないで離した状態にして電界を印加した効果について、強誘電体特性を示す。図中の（イ）は電界を印加していない場合、（ロ）は電極を接触させた状態で電界を印加させた場合、（ハ）は本実施例に基づき、電極を接触させないで離した状態で電界印加した場合である。（ロ）の残留分極値は、（イ）とほぼ同様であり、強誘電体特性の向上が認められなかったが、（ハ）の残留分極値は、（イ）に比べて、大きくなっており、強誘電体特性が向上したのがわかる。電極を接触させないで離した状態で電界を印加することにより、結晶配向性を高めるとともに、強誘電体特性も向上した。
【００１６】
（実施例２）
図７に強誘電体等の酸化物バルク体の製造構造図を示す。ＰｂＯ、ＺｒＯ、ＴｉＯ２粉末原料を混合・成形したＰＺＴについて、図７に示すように、上部電極だけをＰＺＴと接触させないで離した状態にして、熱処理工程中に、電界を印加させた。
【００１７】
それにより、バルク体の結晶配向性を高めるとともに、強誘電体特性も向上した。
【００１８】
【発明の効果】
以上のように、強誘電体等の酸化物膜・バルク体を熱処理するときに、電極を接触させないで離した状態で電界を印加することにより、結晶配向性を高めることができると同時に、リーク電流特性、強誘電体特性等の電気的特性を向上させた強誘電体等の酸化物膜・バルク体を製造することができる。
【図面の簡単な説明】
【図１】強誘電体等の酸化物膜に電界を印加する製造構造概念を示した断面図である。
【図２】強誘電体等の酸化物バルク体に電界を印加する製造構造概念を示した断面図である。
【図３】強誘電体膜にさまざまな角度から電界を印加する製造構造概念を示した断面図である。
【図４】強誘電体等の酸化物薄膜に電界を印加する製造構造を示した断面図である。
【図５】強誘電体薄膜のＸ線回折図である。
【図６】強誘電体薄膜の強誘電体特性を示した図である。
【図７】強誘電体のバルク体に電界を印加する製造構造を示した断面図である。
【符号の説明】
１ 上部電極
２ 強誘電体等の酸化物膜
３ 下部電極
４ 基板
５ 電圧発生装置
６ 熱処理炉
７ 強誘電体等の酸化物バルク体[0001]
TECHNICAL FIELD OF THE INVENTION
In the present invention, when heat treatment is performed on an oxide material such as a ferroelectric material, the upper and lower electrodes may be separated from each other without being brought into contact with each other, or an electric field may be applied while only one of the electrodes is separated from the other material. The present invention relates to a manufacturing method for improving the crystal orientation of an oxide material and improving electrical characteristics such as leakage current characteristics and ferroelectric characteristics.
[0002]
[Prior art]
Examples of a method for forming an oxide film such as a ferroelectric substance include a sol-gel method, a sputtering method, an MOCVD method, and a doctor blade method. Among them, the sol-gel method can form an oxide film such as a ferroelectric material most easily and inexpensively. In the sol-gel method, usually, a precursor solution containing a metal alkoxide is formed into a film by spin coating or dip coating, and then subjected to heat treatment in a heat treatment furnace to crystallize. As a heat treatment method, there are a reduced pressure heating method, an atmosphere heating method, a rapid heating method, and the like. However, the crystal orientation of an oxide film such as a ferroelectric substance cannot be controlled by the heat treatment method. An oxide film such as a ferroelectric film formed by a sputtering method, an MOCVD method, or the like may be reheat-treated, but the crystal orientation of the oxide film such as a ferroelectric material cannot be controlled.
[0003]
In the method of manufacturing a ferroelectric thin film described in JP-A-5-85706 and the method of manufacturing an oriented ferroelectric thin film described in JP-A-5-226322, heat treatment is performed while an electric field is applied to the ferroelectric thin film. In the writing, the electrode to which the electric field is applied is applied to the thin film, or a Pt electrode is attached by a sputtering method, and the electric field is applied in a contact state.
[0004]
In the case of an oxide bulk material such as a ferroelectric substance, usually, after mixing and molding a powder raw material, a heat treatment is performed to cause crystallization. As a heat treatment method, there are HIP and rapid heating, but the crystal orientation cannot be controlled.
[0005]
[Problems to be solved by the invention]
According to the above-mentioned conventional heat treatment method, an oxide film or a bulk body such as a ferroelectric material having high crystal orientation and excellent electric characteristics could not be obtained. In the method disclosed in JP-A-5-85706 for manufacturing a ferroelectric thin film and in the method disclosed in JP-A-5-226322 for manufacturing an oriented ferroelectric thin film, an electric field is applied while the electrodes are in contact with each other. Therefore, a ferroelectric thin film having a certain degree of crystal orientation can be obtained, but current easily flows in the thin film, and the quality of the film deteriorates due to a leak current. In addition, since the ferroelectric is an oxide, when the electrodes are brought into contact with each other, oxygen cannot be sufficiently supplied to the ferroelectric, and it becomes difficult to form a perovskite phase having ferroelectric characteristics. For these reasons, it is difficult to obtain excellent electric characteristics such as leak current characteristics and ferroelectric characteristics.
[0006]
[Means for Solving the Problems]
An electric field is applied when an oxide film such as a ferroelectric film formed on the lower electrode is heat-treated by a sol-gel method, a sputtering method, an MOCVD method, a doctor blade method, or the like. As a method of applying an electric field at this time, the upper electrode is not in contact with an oxide film such as a ferroelectric substance, but in a separated state, and has a structure in which only an electric field can be applied so that no current flows through the film. .
[0007]
An electric field is applied when heat-treating a bulk oxide material such as a ferroelectric material obtained by mixing and molding a powder raw material. As a method of applying an electric field at this time, the bulk material such as a ferroelectric material is separated from the upper and lower electrodes without contacting the upper and lower electrodes, or performed with only one of the electrodes separated. The structure is such that only an electric field can be applied so that no current flows.
[0008]
[0006] As a method of applying an electric field to an oxide thin film such as a ferroelectric material described in [1], an upper electrode is arranged in various directions with respect to an oxide film such as a ferroelectric material, and an electric field is applied in various directions. A structure that can be applied can be adopted.
[0009]
[0006]
[0007]
In the method for applying an electric field described in the above, the time for applying the electric field may be only when the oxide material such as a ferroelectric is crystallized, or throughout the entire heat treatment process. The temperature may be raised at any time, maintained at the crystallization temperature, or lowered at any time.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a conceptual diagram of an electric field application structure of an oxide film such as a ferroelectric substance.
Examples of a method for forming an oxide film such as a ferroelectric substance include a sol-gel method, a sputtering method, an MOCVD method, and a doctor blade method. Among them, the sol-gel method can form an oxide film such as a ferroelectric material most easily and inexpensively. An electric field is applied when the film formed on the lower electrode by the sol-gel method is heat-treated. As a method of applying an electric field at this time, the upper electrode is separated from the oxide film such as a ferroelectric material without being in contact with the oxide film. By doing so, not only can the crystal orientation of the film be enhanced, but also only an electric field can be applied to the film, so that no current flows through the film and the film quality is improved. Further, since the separation is performed, oxygen can be sufficiently supplied to the film, and a perovskite phase is easily formed. From these facts, a film having a high crystal orientation and a uniform polarization direction can be obtained, and at the same time, a film having excellent electric characteristics such as leak current characteristics and ferroelectric characteristics can be obtained. In the case where an oxide film such as a ferroelectric film formed by a sputtering method, an MOCVD method, or the like is reheat-treated, a film having a high crystal orientation and a uniform polarization direction can be obtained by the above method. Thus, a film having excellent electric characteristics such as a leak current characteristic and a ferroelectric characteristic can be obtained.
[0011]
FIG. 2 shows a conceptual diagram of an electric field application structure of an oxide bulk body such as a ferroelectric substance.
An electric field is applied when heat-treating a bulk oxide such as a ferroelectric obtained by mixing and molding a powder raw material. As a method of applying an electric field at this time, a method is used in which a bulk oxide such as a ferroelectric material is applied with only one of the electrodes separated as shown in FIG. 2A, or as shown in FIG. When the electrodes are separated from each other without contacting the upper and lower electrodes, not only can the crystal orientation of the bulk body be aligned, but also only the electric field can be applied to the bulk body. Characteristics are also improved. Further, since the separation is performed in a separated state, oxygen can be sufficiently supplied to the bulk body, and a perovskite phase is easily formed. From these, a bulk body having a high crystal orientation and a uniform polarization direction and excellent electric properties can be obtained.
[0012]
FIG. 3 is a conceptual diagram of a structure in which an upper electrode is arranged in various directions with respect to an oxide film such as a ferroelectric substance, and an electric field can be applied in various directions.
The upper electrode is arranged at various positions in a state in which the upper electrode is separated from the ferroelectric film formed on the lower electrode by a sol-gel method or the like without contacting the ferroelectric film. By applying an electric field during firing in this state, a film having a desired crystal orientation can be obtained, and at the same time, a film having excellent electric characteristics such as leak characteristics and ferroelectric characteristics can be obtained.
[0013]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
(Example 1)
FIG. 4 shows an electric field application structure diagram of an oxide thin film such as a ferroelectric substance. A Pb 1.2 La 0.1 TiO 3 (PLT) thin film was formed by spin coating on a substrate on which platinum (Pt) was formed by a sputtering method, and dried and calcined. Spin coating, drying, calcining is performed repeatedly to obtain a thin film of about 250nm. As shown in FIG. 4, the obtained thin film was placed in a state of being separated by 0.5 mm without contacting the upper electrode and the Pb 1.2 La 0.1 TiO 3 thin film, and was subjected to a heat treatment process at 500 ° C. in the air. , An electric field of 5 V was applied.
[0014]
FIG. 5 shows an X-ray diffraction diagram showing the effect of applying an electric field in a state where the electrodes are separated from each other without contact during the heat treatment process. In the figure, (a) shows the case where no electric field is applied, and (b) shows the case where the electric field is applied according to the present embodiment. Obviously, the peak of (100) of the PLT is stronger in (b). It turns out that the crystal orientation is high.
[0015]
FIG. 6 shows the ferroelectric characteristics of the effect of applying an electric field in a state where the electrodes are separated without contact during the heat treatment step. In the figure, (a) shows the case where no electric field is applied, (b) shows the case where the electric field is applied in a state where the electrodes are in contact, and (c) shows the case where the electrodes are separated without contact based on the present embodiment. This is the case where an electric field is applied in this state. The remanent polarization value of (b) was almost the same as (a), and no improvement in the ferroelectric properties was observed. However, the remanent polarization value of (c) was larger than that of (a). It can be seen that the ferroelectric characteristics were improved. By applying an electric field in a state where the electrodes are not in contact with each other and separated, the crystal orientation is improved and the ferroelectric characteristics are also improved.
[0016]
(Example 2)
FIG. 7 shows a manufacturing structure diagram of an oxide bulk body such as a ferroelectric substance. As shown in FIG. 7, with respect to PZT obtained by mixing and molding PbO, ZrO, and TiO 2 powder raw materials, an electric field was applied during the heat treatment step with only the upper electrode being separated from the PZT without being brought into contact with the PZT.
[0017]
Thereby, the crystal orientation of the bulk body was improved, and the ferroelectric properties were also improved.
[0018]
【The invention's effect】
As described above, when heat treatment is performed on an oxide film or bulk body such as a ferroelectric substance, by applying an electric field in a state in which the electrodes are not in contact with each other, the crystal orientation can be improved, and at the same time, the leakage can be improved. An oxide film or a bulk body such as a ferroelectric material having improved electric characteristics such as current characteristics and ferroelectric characteristics can be manufactured.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the concept of a manufacturing structure for applying an electric field to an oxide film such as a ferroelectric substance.
FIG. 2 is a cross-sectional view showing a manufacturing structure concept for applying an electric field to a bulk oxide body such as a ferroelectric substance.
FIG. 3 is a cross-sectional view showing the concept of a manufacturing structure for applying an electric field to the ferroelectric film from various angles.
FIG. 4 is a sectional view showing a manufacturing structure for applying an electric field to an oxide thin film such as a ferroelectric substance.
FIG. 5 is an X-ray diffraction diagram of a ferroelectric thin film.
FIG. 6 is a diagram showing ferroelectric characteristics of a ferroelectric thin film.
FIG. 7 is a sectional view showing a manufacturing structure for applying an electric field to a ferroelectric bulk body.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 upper electrode 2 oxide film such as ferroelectric 3 lower electrode 4 substrate 5 voltage generator 6 heat treatment furnace 7 bulk oxide such as ferroelectric